Re: Steering rig, VP hinge stiffness

From: Bill Gowen <wdgowen_at_gmail.com>
Date: Tue, 17 Aug 2010 12:00:59 -0400

Tapio
I'll leave most of these answers to people more qualified but here are some personal feelings.

The VP mechanisms that I've seen are incredible at managing energy delivery at such a low weight penalty. However most of them are pretty crude mechanically. There are just not good options for low friction bearings in these designs. Consequently the mechanisms tend to move in steps as you've already observed. I don't think the normal vibration from an unwinding motor is enouigh to smooth out the steps. In my opinion the VP normally only moves when then torque drops enough for the spring to overcome the friction in the mechanism. Others have commented on this effect. Larry Coslick has talked about his model starting to bump the ceiling after a steer when it was in a good cruise before the steer.

It isn't too hard to figure this out. A VP test rig can be easily built that will let you observe how the VP changes as torque drops off. Better yet you can set up a rig that will let you photograph the prop blades as a motor unwinds. I'm getting ready to do this with my flaring props for F1L to find out why I had so much trouble at USIC this year.

Static tests won't exactly duplicate what happens in the air but they beat guessing.

Larry Loucka gave me a great tip about balloon lines. He said to use one of the high visibility yellow braided lines so that you can easily see the line below the foam rod. This hasn't made me good at steering but I can see my misses better now!

  ----- Original Message -----
  From: Tapio Linkosalo
  To: Indoor_Construction_at_yahoogroups.com
  Sent: Tuesday, August 17, 2010 10:34 AM
  Subject: [Indoor_Construction] Steering rig, VP hinge stiffness


    

  First of all, greetings from Belgrade. It was great to meet again many
  old friends, and make a number of new, I will not start listing names as
  I would skip someone and then would need to be ashamed.... Anyway, the
  contest was hot and tough, I did not do so good, but I think I learned a
  lot, so now I have lots of homework to do.

  Two questions raised:
  - what sort of line would be good for the steering balloon? I had a foam
  rod between the balloon and the line, but the line that I used was quite
  thin monofilament. For fine handling it was not too pleasant, but I feel
  that some braided stuff would feel more comfy for the fingers. But
  should it be elastic (like dacron), or as stout as possible (dyneema)?
  Is it getter to have a tight contact with the balloon, or line that can
  dampen some impulses? Further: I had glued some thin dyneema within the
  foam rod to take the load, but my thinned contact glue did hot hold the
  line in the slot, any suggestions for a good glue for this application.

  - another question rises from two observations. First, on my best flight
  my model reached top height, then descended maybe 5 meters rather
  rapidly before settling down to much better cruise. Also I heard
  reported that on some steers, mr. Tregers model actually started
  climbing after the steer. A common explanation for both these event
  could be, if the prop hinges were "holding" a little, in the same manner
  as you need to tap the mechanical barometer to see if air pressure is
  changing; for my flight the prop may have "jumped" to the better
  setting, and for Treger the steering might have bumped the prop to lower
  pitch? Does this happen in F1D, or does the rubber unknotting give
  enough "tapping" to make the hinges move freely?

  -Tapio-


  
Received on Tue Aug 17 2010 - 09:34:59 CEST